The present invention is directed to a device driven by a motor receiving electricity from an inverter and repeatedly operated in a same load pattern. Hereinafter, such a device is called a “same load pattern device”.
Herein, same load pattern devices include, but are not limited to, industrial devices such as a servo press, a die cushion for a press, a transfer device and a material handling device.
The amount of loss in the above-described same load pattern device varies with parameters of a power conversion circuit such as a carrier wave frequency and a voltage change rate dv/dt of a switching waveform.
The “amount of loss” herein means the difference between the electric power the inverter receives and the mechanical power the motor outputs, i.e., the amount of work lost as heat generation and electromagnetic radiation in the electric circuit (including the inverter and the motor) ranging from the inverter to the motor and in the magnetic circuit inside the motor.
As means for reducing this amount of loss, Patent Document 1 has been already proposed, for example. As techniques relating to the present invention, Patent Document 2 and Non-Patent Documents 1 and 2 have been disclosed.
Patent Document 1 discloses a technique of, when an operating condition of a device is changed, reducing the amount of loss by changing a parameter of electric power conversion (a carrier wave frequency of a DC/DC converter).
Non-Patent Document 2 discloses a technique of reducing the loss by selecting a different switching frequency during operation in accordance with the operating speed categorization into low-speed level, medium-speed level and high-speed level.